1. Field of the Invention
The invention relates to a fluid supply systems, to a solid-phase adsorbent material useful for storing and dispensing fluids of low vapor pressure, and to a solid-phase sorbent material useful for storing and dispensing liquefied fluids.
2. Description of the Related Art
In a wide variety of industrial processes and applications, there is a need for a reliable source of process fluids. Such process and application areas include, but are not limited to, semiconductor manufacturing, ion implantation, manufacture of flat panel displays, medical intervention and therapy, water treatment, emergency breathing equipment, welding operations, space-based delivery of liquids and gases, etc.
Conventionally, processing fluids are supplied for commercial applications by means of high-pressure cylinders containing compressed processing fluids. However, such conventional high-pressure gas cylinders are susceptible to leakage from damaged or malfunctioning regulator assemblies, as well as to rupture if internal decomposition of the gas leads to rapid increase of interior gas pressure in the cylinder. These deficiencies pose a risk of unwanted bulk release of gas from the cylinder. Such bulk release in turn can create very hazardous and even catastrophic conditions where toxic or otherwise hazardous fluids are involved, particularly during transportation and shipment of fluid cylinders when back-up scrubbing or other safety systems may not be present.
To overcome these inherent problems of high-pressure gas cylinders, sorbent-based fluid storage and dispensing systems may be employed, of the type disclosed in U.S. Pat. No. 5,518,528, issued May 21, 1996 in the names of Glenn M. Tom and James V. McManus. Such sorbent-based fluid storage and dispensing systems effectively reduce the interior gas pressure by reversibly adsorbing sorbate fluid onto a physical sorbent medium disposed inside a containment vessel.
Sorbent-based fluid storage and dispensing systems of such type significantly reduce the risk of gas leakage and cylinder rupture associated with conventional high-pressure gas cylinders. These systems typically utilize physical sorbent materials, such as silica, carbon molecular sieves, alumina, polymers, kieselguhr, carbon, and aluminosilicates, having average pore sizes in a range of from 4 Angstroms to 13 Angstroms. Although these sorbent materials of such pore size character are effective for reducing pressure of certain high vapor pressure fluids (e.g., AsH3, PH3, and BF3), they are not satisfactory for purpose of storing and delivering fluids of low vapor pressures (i.e. <200 psig at room temperature), especially the reactive fluids, for the following reasons.
First, such sorbent materials are chemically incompatible with low vapor pressure gases such as ClF3, WF6 and Br2, reacting with the gases to form unwanted byproducts.
Further, such conventionally employed sorbent materials, due to their respective pore size distributions, are oftentimes characterized by adsorption potentials that are too high. They cannot effectively desorb low vapor pressure gases from the sorbent, and therefore are inadequate to deliver low vapor pressure gases to the tool under normal application conditions. The term “normal application conditions” is hereby defined as fluid delivery conditions characterized by a decrease of pressure from 650 torr to 10 torr at room temperature.
For example, sorbent materials of the type disclosed by the Tom et al. patent, which are characterized by (1) average pore sizes in the range of 4–13 Angstroms and (2) porosity in the range of 30–40%, measured as [gross volume of sorbate/gross volume of sorbent material including voids]×100%, are only able to desorb 10–20% of the low vapor pressure gases such as Br2 under normal application conditions, while the same sorbent materials can desorb 70–90% of the high vapor pressure gases such as arsine (AsH3) and phosphine (PH3).
U.S. Pat. No. 6,089,027, issued Jul. 18, 2000 in the names of Luping Wang and Glenn M. Tom, describes an improved gas storage and dispensing system for storage and dispensing of low vapor pressure liquefied gases such as ClF3, WF6, GeF4, and Br2, etc., in which a fluid pressure regulator is disposed inside of the fluid storage and dispensing vessel. The fluid pressure regulator functions as a flow control device, which can be set at a predetermined pressure level, to dispense fluids from the vessel at such pressure level. Such “regulator in a bottle” arrangement provides an effective system for storage and dispensing of liquids and gases at pressure levels that vary from about 50 psig to about 5000 psig, depending on the specific end use application. When the pressure is set at a subatmospheric level, it can effectively eliminate the hazards of gas leaking out of the vessel in case of development of an external leak during cylinder transportation. The “regulator in a bottle” arrangement is also ideal for safe storage and delivery, of very low vapor pressure (less than 14.7. psia) pyrophoric organometalllic fluids such as trimethyl aluminum, dimethyl aluminum hydride, etc. When storing pyrophoric fluids of very low vapor pressure, the “regulator in a bottle” arrangement with the subatmospherical setting can effectively prevent air from leaking into the cylinder if an external leak develops during cylinder transportation and handling, therefore eliminating the potential fire and other hazards caused by reaction between the pyrophoric fluids and the air.
However, when the fluid storage and dispensing vessel of Wang et al. patent is used for liquefied gases, the fluid pressure regulator is susceptible to malfunction, because liquefied gases can easily enter the regulator and cause discharge pressure instability. In applications such as semiconductor manufacture, the maintenance of precisely controlled flow characteristics (temperature, pressure, flow rate and composition) is critical to the achievement of satisfactory product microelectronic device structures. In such applications, the pressure instability incident to liquid ingress to the regulator compartment causes the occurrence of process perturbations that may render the product microelectronic device structure unsatisfactory or even wholly useless for its intended purpose.
Moreover, during the fluid delivery process, significant cooling occurs when the liquefied gas is evaporated from the storage cylinder, due to the heat loss of vaporization. The cooling will significantly reduce the vapor pressure of the liquefied gas, resulting in insufficient evaporation and slowing down gas flow from the cylinder. One or more heat-exchange units are usually provided on the external wall of the cylinder, for externally supplying thermal energy to the liquefied gas to compensate for the heat loss caused by evaporation. However, the conventional sorbent materials have low thermal conductivities and are therefore ineffective for transfering beat to the liquefied gas inside the cylinder. Insufficient heat transfer causes uneven distribution of thermal energy in different portions of the cylinder, i.e., overheating of the exterior of the cylinder and underheating of the interior of the cylinder.
The art has not found a solution to the above-described problems associated with low vapor pressure fluids or liquefied gases, with respect to sorbent materials having good sorptive affinity, good capacity loading characteristics, good chemical stability, good desorption characteristics, good thermal conductivity, or of liquid containment and occlusion from the regulator element in internal regulator-based fluid storage and dispensing systems.
There is accordingly a need in the art for a physical sorbent material that is chemically compatible with low vapor pressure fluids, that has an adequate pore size, porosity and pore size distribution to reduce storage pressure of low vapor pressure gases via reversible adsorption of such gases, and that enables the sorbate fluid to be readily desorbed from the physical adsorbent material for discharge from the vessel during dispensing operation.
There is concurrently a need in the art for a solution for the liquid ingress problems associated with the use of internal regulator-based fluid storage and dispensing systems.